Monoclonal antibodies directed against the microtubule-associated protein tau, and hybridomas secreting these antibodies

ABSTRACT

The invention relates to a monoclonal antibody AT 120 which forms an immunological complex with an epitope of an antigen belonging to normal human tau protein as well as abnormally phosphorylated human tau protein, with said tau protein being liable to be obtained from a brain homogenate, itself isolated from human cerebral cortex. The monoclonal antibodies of the invention can be used to detect tau and abnormally phosphorylated tau in brain extracts and in unconcentrated cerebrospinal fluid.

PRIOR APPLICATIONS

The present application is a continuation-in-part of PCT application No. EP93/03499 filed Dec. 10, 1993 claiming the priority of European patent application Ser. No. 92-403403.6 filed Dec. 14, 1992.

The invention relates to new monoclonal antibodies directed against the human microtubule-associated protein tau, to the hybridomas secreting these monoclonal antibodies, and to the antigen recognition by these monoclonal antibodies and their applications. The invention also relates to a process for diagnosing brain diseases involving the particular epitope (of the tau protein) which is recognized by said monoclonal antibodies.

Alzheimer's disease (AD) is the most common form of adult-onset dementia. At present, no biochemical test is available for antemortem diagnosis of AD. The disease is therefore clinically diagnosed primarily by exclusion of other forms of dementia. The illness is characterized neuropathologically by the presence of neuritic (senile) plaques and neurofibrillary tangles (NFT).

Neurofibrillary tangles consist of paired helical filaments (PHF), of which the main protein component is a modified form of the microtubule-associated protein tau (Brion et al., 1985; Greenberg and Davies, 1990; Lee et al.,1991), which under normal circumstances promotes microtubule assembly and stability (Weingarten et al., 1975; Bre and Karsenti, 1990), which is synthesized in the neurons of several species, including humans (Kosik et al., 1989) and which is abundantly present in the axonal compartment of these neurons (Binder et al., 1985).

The protein exists as a family of different isoforms of which 4 to 6 isoforms are found in normal adult brain but only 1 isoform is detected in fetal brain (Goedert et al., 1989). The diversity of the isoforms is generated from a single gene by alternative mRNA splicing (Himmler, 1989). The most striking feature of tau protein, as predicted from molecular cloning, is a stretch of 31 or 32 amino acids occurring in the carboxy-terminal part of the molecule that is repeated 3 or 4 times. Additional diversity is generated through 29 or 58 amino acid-long insertions in the NH₂ -terminal part of the molecules (Goedert et al., 1989).

Tau variants of 64 and 69 kDa, which are abnormally phosphorylated, as revealed by the apparent increase in their molecular mass observed after alkaline phosphatase treatment, have been detected exclusively in brain areas showing neurofibrillary tangles and senile plaques (Flament et al., 1989, 1990). The sites of phosphorylation by 4 different kinases have been mapped in the C-terminal microtubule-binding half of tau, and it could be shown that the action of a calcium calmodulin-dependent kinase on bacterially expressed tau resulted in the phosphorylation of Ser(405) which induced a lower electrophoretical mobility (Steiner et al., 1990). Tau present in paired helical filaments, called PHT-tau is abnormally phosphorylated (Lee et al., 1991). This abnormal phosphorylation causes a conformational change in tau, resulting probably in self-association and the formation of PHFs. PHF-tau in AD is phosphorylated at several sites, one of which is the phosphoserine 199 and/or 202. This site is specifically recognized by a mAb called AT8 (Biernat et al., 1992). Therefore, AT8 is a discriminative marker for PHF-tau (Goedert et al., 1992).

Several antibodies have been reported that show reactivity to human tau either because they are directed to non-specific phosphorylated epitopes present on neurofilament and subsequently shown to cross-react with normal and abnormally phosphorylated tau (Nukina et al., 1987; Ksiezak-Reding et al., 1987) or because they recognized specific epitopes on normal and abnormally phosphorylated tau (Kosik et al., 1988). In addition to the tau antibodies directed towards non-specific epitopes, antibodies directed specifically to phosphorylated tau epitopes have been described (Mercken et al., 1992b).

Although overall tau mRNA levels are only slightly modulated in Alzheimer-affected brain regions (Goedert et al., 1988; Barton et al., 1990) it has been shown that total tau protein levels may differ at least 6-fold (Khatoon et al., 1992). This has been demonstrated by polyclonal antibodies against tau (Flament and Delacourte, 1990) and by monoclonal antibodies directed to well-defined epitopes. The Alz 50 monoclonal antibody recognizing a phosphate-independent epitope in the N-terminus of the tau molecule (Goedert et al., 1991) has been used in a sandwich immunoassay on brain homogenates and it has been shown that tau levels are higher in Alzheimer's patient brains (Ghanbari et al., 1990; patent application EP 444 856).

An antibody named "423", raised against pronase-treated PHFs and specifically reactive with a 9.5 kDa and a 12 kDa fragment was also used to measure tau protein in Alzheimer's disease (patent application WO 89/03993). Similarly, it was found that increased mAb 423 immunoreactivity was observed in Alzheimer brain homogenates as compared with control brain homogenates.

Mercken et al. (1992b) describe a range of monoclonal antibodies which are either specific for a phosphatase-sensitive epitope (AT8) or which react with PHF-tau as well as with normal tau (AT1, AT4, AT6, AT9, AT 11, AT12 and AT14) in Western blotting.

Moreover, the antibody tau 1 (Wischik et al., 1988; Harrington et al., 1990) was also used to measure tau in brain homogenates. In one case when tau levels were specifically measured in Alzheimer-affected brain sections, tau levels were eight-fold higher as compared with levels in normal brain homogenates (Khatoon et al., 1992).

In a first attempt to diagnose Alzheimer disease in cerebrospinal fluid, the PHF-tau-specific monoclonal antibody AT8 (Mercken et al., 1992b), was used. However, no PHF tau antigen could be demonstrated.

Thus far, none of the monoclonals that have been described have been successful in detecting tau in non-concentrated cerebrospinal fluid (CSF), although the presence of tau was observed in 100-fold concentrated CSF (Wolozin and Davies, 1987) or in CSF samples using polyclonal antibodies (Delacourte and Vermersch, 1991).

The aim of the present invention is therefore to provide monoclonal antibodies which allow reliable and sensitive detection of normal and abnormally phosphorylated tau present in brain extracts and in unconcentrated cerebrospinal fluid. The invention also aims at providing the hybridoma which secretes the above-said monoclonal antibodies.

The invention furthermore aims at providing the epitope of the tau protein present in brain homogenates or in body fluids such as cerebrospinal fluid, which is recognized by said monoclonal antibodies.

The invention aims at providing a process for the detection or diagnosis in vitro of brain diseases involving tau protein.

The monoclonal antibodies of the invention are characterized by the fact that they react with an epitope which is present in both normal and abnormally phosphorylated human tau protein. The monoclonal antibodies are furthermore characterized by the fact that they form an immunological complex with an epitope or an antigen belonging to normal and abnormally phosphorylated human tau protein. The monoclonal antibodies of the invention are also characterized by the fact that they do not form an immunological complex with other phosphorylated proteins such as MAP-1, MAP-2 and neurofilaments which share part of their sequence with tau protein (Nukina et al., 1987; Lewis et al., 1988) as determined by means of an ELISA. The monoclonal antibodies of the invention are also characterized by the fact that they are liable to detect human tau protein in CSF, with said tau protein being at a concentration as low as 1.0 pg/ml and with said tau protein being detected at 100% recovery upon the addition of a fixed amount of tau protein in tau protein-negative CSF (100% spiking recovery).

The monoclonal antibodies of the invention also enable the diagnosis of Alzheimer's disease (AD) on the basis of CSF, i.e., to detect tau and modified forms of tau in CSF. The problem associated herewith is that this antigen is present in a very low amount in CSF, therefore the detection assay must be very sensitive. This problem can be resolved by using the combination of the monoclonal antibody of the invention together with the catalysed reporter deposition amplification technique (CARD, Bobrow et al., 1989), allowing a tau-specific CARD ELISA with a higher sensitivity. Alternatively, a mixture or combinations of labeled monoclonal antibodies, each recognizing epitopes different from AT120 epitope, could be used as detector antibodies.

The results obtained with the monoclonal antibody secreted by the hybridoma AT120 of the invention indicate that elevated tau levels are not only found in AD, but also in other neurological diseases where neuronal death or damage occurs.

The expression "form an immunologically complex with" means that the monoclonal antibody of the invention binds to the above-said antigen under one of the following conditions as mentioned in the techniques below:

Light immunomicroscopy

Brain tissue samples, obtained at surgery or autopsy, are fixed by immersion in 4% formalin or Bouin's fixative and embedded in paraffin for sectioning. The monoclonal antibodies of the invention are applied in conjunction with a technique to visualize the formed immune complexes such as the avidin-biotinylated peroxidase complex technique (Hsu et al., 1981) using 3,3'-diaminobenzidine tetrahydrochloride for development of color. Sections are counterstained with Harris haematoxylin stain.

Immunoelectron microscopy in tissue sections

Brain tissue samples, obtained at surgery or autopsy are fixed in either Bouin's fixative or 10% buffered formalin before sectioning without embedding (Vibratome). The monoclonal antibody of the invention is used for immunostaining by the indirect immunogold method after which the sections are fixed, embedded and sectioned for electron microscopy, all according to standard protocols known to those skilled in the art (Brion et al., 1985).

Immunoblotting procedures

For immunoblotting, fractions enriched in tau are prepared as described (Lindwall and Cole, 1984). Typically, 50 g of brain tissue is cut into small pieces with scissors and homogenized 1:1 (wt/vol) in buffer A (20 mM 2- N-morpholino!ethanesulfonic acid, 80 mM NaCl, 2 mM EDTA, 0.1 mM EGTA, 1 mM β-mercaptoethanol, pH 6.75) with a Potter homogenizer equipped with a Teflon plunger. The homogenate is centrifuged for 1 h at 150,000 g at 4° C., and the supernatant is heated for 5 min in boiling water and chilled again for 10 min on ice. The slurry is centrifuged for 2 h at 150,000 g at 4° C., and the supernatant is collected. The heat-stable cytosolic extract is added to 2.5% perchloric acid and centrifuged for 1 h at 150,000 g at 4° C., after which the supernatant is neutralized with 3M Tris. The supernatant is then dialyzed in water and concentrated in a Centriprep concentrator (Amicon, Lausanne, Switzerland).

SDS-polyacrylamide electrophoresis is performed under reducing conditions on 12% gels (Laemmli, 1970). After electrophoresis, the proteins are either fixed and stained with Coomassie brilliant blue, or transferred (Towbin et al., 1979) to nitrocellulose sheets (Hybond-C, Amersham) or Immobilon filters (Millipore).

After transfer, the filters are presoaked in PBS containing 0.05% (v/v) Tween 20 (Tween-PBS) and then incubated for 1 h in Tween-PBS containing 5% (w/v) skimmed dried milk and 10% (v/v) newborn calf serum (blocking buffer). Next, the filters are treated overnight at 4° C. with a monoclonal antibody according to the invention appropriately diluted in blocking buffer.

The filters are then washed three times in Tween-PBS and treated for 1.5 h at room temperature with horseradish peroxidase-labeled rabbit anti-mouse IgG (Dakopatts, Denmark) diluted 1/3000 in blocking buffer. After three washes in Tween-PBS, streptavidine-biotinylated horseradish peroxidase complex (Amersham), diluted 1/250 in blocking buffer, is applied for 1.5 h at room temperature. Thereafter, the filters are washed three times in Tween-PBS and once in PBS. The filters are then incubated in PBS containing 0.05% (w/v) diaminobenzidine and 0.03% (v/v) hydrogen peroxide until background staining develops.

It should be clear that the formation of an immunological complex between the monoclonal antibodies and the antigen is not limited to the precise conditions described above, but that all techniques that respect the immunochemical properties of the antibody and antigen binding will produce similar formation of an immunological complex.

Human normal tau is a class of at least six tau proteins ranging in molecular weight from 58 to 64 kDa which are specifically expressed in the somatodendritic domain of all neurons (Papasozomenos and Binder, 1987). Moreover Alzheimer (tangle)-specific tau forms have been described which occur in the degenerating cortical neurons of Alzheimer's disease or Down's Syndrome and of which the lower electrophoretic mobility can be attributed to abnormal phosphorylation (Flament et al., 1989; Delacourte et al., 1990).

According to an advantageous embodiment of the invention, the monoclonal antibody forms an immunological complex with all forms of tau described above, with said human tau protein being liable to be obtained from a brain homogenate, itself isolated from the cerebral cortex of a patient suffering from a neurological disease.

A "brain homogenate" and tau protein can be obtained by the man skilled in the art according to standard methods such as the method of Lindwall and Cole (1984).

According to an advantageous embodiment, the monoclonal antibodies of the invention form an immunological complex:

either with an epitope located within the following amino acid sequence of human tau protein: ##STR1## most specifically with an epitope located within the following amino acid sequence: ##STR2## or with any other peptide capable of forming an immunological complex with a monoclonal antibody, which is capable of forming a complex with an epitope located in a tau protein regions as shown in any of SEQ ID NO 1 to 3.

The sequences as shown in SEQ ID NO 1 to 3 will be hereafter designated as containing "the epitope" of the invention. Amino acid sequence I spans the amino acid 155-221 of human tau using the numbering of human tau 40 , amino acid sequence 2 spans the amino acid 199-231 of human tau and amino acid sequence 3 spans the amino acid 199-221 of human tau (Goedert et al., 1989).

The peptides capable of forming an immunological complex with a monoclonal antibody, which itself is liable to form a complex with the above-mentioned peptide will be defined as the "variant peptides".

A preferred monoclonal antibody of the invention is secreted by the hybridoma deposited at ECACC (European Collection of Animal Cell Cultures, Vaccine Research and Production Laboratory, Public Health and Laboratory Service (PHLS), Center for Applied Microbiology and Research, Proton Down, GB-Salisbury, Wiltshire SP4 OJG) on Oct. 8, 1992 under No. 92100853.

This hybridoma will be hereafter designated as "hybridoma AT120" and the secreted monoclonal antibody will be designated as "monoclonal antibody AT120".

The invention also relates to the hybridoma which secretes a monoclonal antibody according to the invention, and particularly the hybridoma filed at ECACC on Oct. 8, 1992 under No. 92100853.

The above-mentioned monoclonal antibodies are obtained by a process involving obtention and isolation of hybridomas which secrete these monoclonal antibodies.

A process for obtaining the hybridoma involves:

starting from spleen cells of an animal, e.g. mouse or rat, previously immunized in vivo, or from spleen cells of such cells previously immunized in vitro with an antigen recognized by the monoclonal antibody deposited at ECACC on Oct. 8, 1992 under No. 92100853, or with a peptide containing or which are constituted by parts of any of the sequences as represented in SEQ ID NO 1 to 3;

fusing said immunized cells with myeloma cells under hybridoma-forming conditions; and

selecting those hybridomas which secrete the monoclonal antibodies which specifically recognize an epitope of the above-said antigen and which form an immunological complex with normal tau or the abnormally phosphorylated form of tau protein or with the peptide comprising the epitope of tau recognized by the monoclonal antibody of the invention.

A process for producing the corresponding monoclonal antibodies involves:

culturing the selected hybridoma as indicated above in an appropriate culture medium; and

recovering the monoclonal antibodies secreted by said selected hybridoma; or alternatively

implanting the selected hybridoma into the peritoneum of a mouse and, when ascites has been produced in the animal;

recovering the monoclonal antibodies then formed from said ascites.

The monoclonal antibodies of the invention can be prepared by conventional in vitro techniques such as the culturing of immobilized cells using e.g. hollow fibers or microcapsules or such as the culturing of cells in homogeneous suspension using e.g. airlift reactors or stirred bioreactors.

The invention also relates to a peptide (antigen), which can be obtained from a human brain homogenate itself being isolated from the human cerebral cortex obtained from a patient having Alzheimer's disease, and which forms an immunological complex with the monoclonal antibody of the invention.

The invention also relates to peptides (antigens) which are liable to form an immunological complex with anyone of the monoclonal antibodies of the invention and

which are contained in or are constituted by parts of the sequence as shown in SEQ ID NO 1;

which contain or are constituted by the sequence of the variant peptides defined above.

It is to be recalled that variant peptides are those peptides able to form an immunological complex with a monoclonal antibody, which itself is liable to form a complex with an epitope located in the tau protein region as shown in SEQ ID NO 1 to 3.

The invention also relates to polypeptides (antigens) of about 100 amino acids

which contain the sequence as shown in SEQ ID NO 1 to 3 , or

which contain the sequence of the variant peptides defined above.

The invention also relates to the above- mentioned peptides which are liable to generate monoclonal antibodies of the invention.

The invention also relates to a peptide (antigen) which is contained in the brain, in the cerebrospinal fluid, or in the serum of a patient having Alzheimer's disease or any brain disease involving normal human tau protein and which forms an immunological complex with a monoclonal antibody of the invention.

The invention also relates to a peptide (antigen) which is contained in the brain, in the cerebrospinal fluid, or in the serum of a patient having Alzheimer's disease or any brain disease involving PHF or abnormally phosphorylated human tau protein and which forms an immunological complex with a monoclonal antibody of the invention.

A method for preparing the peptides of the invention is characterized in that, preferably starting from the C-terminal amino acid, the successive aminoacyls in the requisite order, or aminoacyls and fragments formed beforehand and already containing several aminoacyl residues in the appropriate order, or alternatively several fragments prepared in this manner beforehand, are coupled successively in pairs, it being understood that care will be taken to protect all the reactive groups carried by these aminoacyls or fragments beforehand except for the amine groups of one and carboxyl groups of the other, or vice versa, which must normally participate in peptide bond formation, in particular after activation of the carboxyl group, according to methods known in peptide synthesis, and so on, proceeding stepwise up to the N-terminal amino acid.

The antigen of the invention, which can be prepared by methods known to those skilled in the art (Lindwall and Cole, 1984) starting from the human cerebral cortex is characterized by its ability to form an immunological complex with the monoclonal antibody of the invention as defined above, advantageously with the monoclonal antibody secreted by the hybridoma AT120 deposited at the ECACC Wiltshire, United Kingdom under No. 92100853 on Oct. 8, 1992.

The antigen of the invention is advantageously contained in the brain, in the cerebrospinal fluid or the serum of a patient having Alzheimer's disease, Down syndrome, Pick's disease, subacute sclerosing panencephalitis (SSPE) or other neurological diseases in which the normal tau or abnormally phosphorylated tau protein are implicated; this antigen provokes an immunological reaction with the monoclonal antibody of the invention.

The invention also relates to a process for the detection or the diagnosis in vitro of brain disease involving tau protein, i.e. Alzheimer's disease, which involves:

bringing the monoclonal antibody of the invention into contact with a preparation of NFT containing tau protein or a detergent-extracted brain homogenate containing tau protein isolated from a patient having had Alzheimer's disease or any other disease involving tau protein or abnormally phosphorylated tau protein under conditions suitable for producing an antigen-antibody complex; and,

separating the antigen from said complex and recovering the antigen sought in a purified form.

The preparation of tau can be carried out according to Lindwall and Cole (1984).

Advantageously, the monoclonal antibodies used are in an immobilized state on a suitable support such as a resin. The process for the detection of the antigen can then be carried out as follows:

bringing the supernatant containing proteins and polypeptides obtained as a result of an extraction procedure starting from brain tissues or cerebrospinal fluid known to those skilled in the art (Iqbal et al., 1984; Greenberg and Davies, 1990) into contact with said monoclonal antibody, under such conditions as to allow the formation of an immunological complex;

washing the immobilized antibody-antigen complex then formed;

treating this complex with a solution (e.g. 3M potassium thiocyanate, 2.5M magnesium chloride, 0.2M citrate-citric acid, pH 3.5 or 0.1M acetic acid) capable of producing the dissociation of the antigen- antibody complex; and;

recovering the antigen in a purified form.

The process of the invention for the detection or diagnosis in vitro of brain disease involving tau protein and abnormally phosphorylated tau protein, as e.g. in Alzheimer's disease, includes:

bringing a sample of a brain homogenate, or of cerebrospinal fluid, or of serum from a patient suspected of suffering from a neurological disorder involving tau protein or PHF, more particularly Alzheimer's disease, into contact under in vitro conditions with the monoclonal antibody of the invention, with said conditions being suitable for producing an antigen-antibody complex; and

detecting the immunological binding of said antibody to said sample of brain homogenate, or of cerebrospinal fluid, or of serum.

The detection of the immunologically bound monoclonal antibody can be achieved by conventional technology. Advantageously, the monoclonal antibody of the invention itself carries a marker or a group for direct or indirect coupling with a marker as exemplified hereafter. Also, a polyclonal antiserum can be used which was raised by injecting the antigen of the invention in an animal, preferably a rabbit, and recovering the antiserum by immunoaffinity purification in which said polyclonal antibody is passed over a column to which said antigen is bound and eluting said polyclonal antibodies by conventional technology.

Detection can also be achieved by competition binding of the antigen with a labeled peptide comprising the epitope of the invention.

A particularly advantageous embodiment of the process of the invention for the detection or diagnosis in vitro of brain diseases involving PHF and/or normal tau protein, e.g. Alzheimer's disease, comprises the steps of:

bringing a sample of unconcentrated cerebrospinal fluid sample isolated from a patient suspected of suffering from a neurological disorder involving normal or abnormally phosphorylated tau protein, more particularly Alzheimer's disease, into contact under in vitro conditions with a monoclonal antibody according to the invention, under conditions suitable for producing an antigen-antibody complex;

and,

detecting the immunological binding of said antibody to said sample of cerebrospinal fluid by means of a sandwich ELISA, preferably by applying the catalysed reporter diagnosis enhancement (CARD) procedure.

The invention also relates to a kit for the diagnosis in vitro of one of the following diseases: Alzheimer's disease, Down's syndrome, Pick's disease, subacute sclerosing panencephalitis (SSPE) and other neurodegenerative disorders in which normal tau protein or abnormally phosphorylated tau protein are implicated. Such a kit would contain:

at least one microplate for deposition thereon of any monoclonal antibody of the invention;

a preparation containing the sample to be diagnosed in vitro, possibly together with a labeled peptide containing the epitope of the invention and preferably, a peptide lying in the peptide sequence as shown in SEQ ID NO 1 to 3.

a second antibody

which can be a monoclonal antibody recognizing another epitope of normal or abnormally phosphorylated tau protein, or of any peptide of the invention, with said epitope being different from the one of the invention, or

which can be a polyclonal antibody directed against normal or abnormally phosphorylated tau, or against a peptide of the invention, with said polyclonal antibody being liable to form an immunological complex with epitopes which are all different from the epitope of the invention, with said polyclonal antibody being preferably purified by immunoaffinity chromatography using immobilized tau protein, or

a marker either for specific tagging or coupling with said second antibody;

appropriate buffer solutions for carrying out the immunological reaction between the monoclonal antibody of the invention and a test sample on the one hand, and the bound second antibody and the marker on the other hand.

The labeled peptide mentioned above can be a peptide which has been labeled by any means known for the man skilled in the art. Moreover, the marker specific for tagging and coupling can be any marker known to the man skilled in the art.

The invention also relates to a kit, as described above, also containing the antigen of the invention, with said antigen of the invention being either a standard (for quantitative determination of the antigen which is sought) or a competitor, with respect to the antigen which is sought, for the kit to be used in a competition dosage process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1

Western blotting detection of normal tau or PHF-tau using the monoclonal antibodies Tau-1, (Binder et al., 1985) AT8 (Mercken et al., 1992b) and AT120. Lanes 1, 3 and 5: PHF-tau isolated according to Greenberg and Davies (1990). Lanes 2, 4 and 6: Normal affinity purified human tau according to Mercken et al. (1992a). Lane 7: Molecular weight markers.

Lanes 1 and 2 were developed using AT8, lanes 3 and 4, using AT120 and lanes 5 and 6, using Tau-1 monoclonal antibody.

FIG. 2A and FIG. 2B

Detection of tau protein by immunochemistry

FIG. 2A: section from hippocampus of a patient with Alzheimer's disease. Magnification 212×.

FIG. 2B: section from another hippocampus of a patient with Alzheimer's disease with abundant tangles. Magnification 212×.

FIG. 3

Titration of normal (0) and PHF tau (▪), spiked in a tau-negative CSF pool using the amplified (CARD) AT120 sandwich ELISA. All dilutions were tested in duplicate and the data presented as optical density (OD) units.

FIG. 4

Western blotting of several deletion mutants constructed as indicated in example V, and stained with AT120 as indicated in Example I. Mutants comprise the following amino acids (AA); Lane 1, full length tau 34 (Goedert et al., 1989); Lane 2, amino terminus of tau 34 up to AA₁₅₄ ; Lane 3, from AA₁₅₅ to the carboxyterminus of tau 34; Lane 4; aminoterminus of tau 34 up to AA₂₄₂ ; Lane 5, aminoterminus tau 34 up to AA₂₂₁ ; Lane 6, from AA₂₂₂ to the carboxyterminus of tau 34.

FIG. 5

Epitope recognition sites of the monoclonal antibodies HT7, BT2, AT8 are depicted on the epitope of the invention (SEQ ID NO 1) shown in the one letter amino acid code. Epitopes are boxed. The star "^(*) " designates the fact that the AT8 epitope recognition needs phosphorylation of serine residue 202.

FIG. 6

Complete sequence of the mTHFMPH-tau1 fusion protein with indication of relevant restriction sites (SEQ ID NO: 9 and SEQ ID NO: 10).

EXAMPLES Example I

Preparation of the monoclonal antibody AT120 (IgG1, subtype kappa)

1. Preparation of the antigen for immunization

PHF-tau was partially purified by a modification of the method of Greenberg and Davies (1990). Postmortem tissue, consisting mostly of gray matter from the frontal and temporal cortex, was obtained from histologically confirmed Alzheimer patients. This Alzheimer gray matter brain sample (5-10 g) was homogenized with 10 volumes of cold buffer H (10 mM Tris/1 mM EGTA/0.8M NaCl/10% sucrose, pH 7.4) in a Teflon/glass Potter S (Braun, Germany) homogenizer. After centrifugation of the homogenate in a 60 Ti MSE rotor at 27,000×g for 20 min at 4° C., the pellet was removed and the supernatant was adjusted to 1% (wt/vol) N-laurosylsarcosine and 1% (vol/vol) 2-mercaptoethanol and incubated while rotating on a mixer (Swelab, Sweden) for 2.5 hours at 37° C. The supernatant mixture was centrifuged at 108,000×g for 35 min at 20° C. The PHF-tau containing pellet was gently washed with PBS and finally suspended in 1 ml of the same buffer.

The antigen preparation was evaluated by a 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by Western blotting using immunoblotting with polyclonal rabbit antihuman normal tau antiserum (Mercken et al., 1992b).

2. Immunization protocol and fusion procedure

Balb/c mice were primed subcutaneously with 100 μg partially purified PHF-tau in complete Freund's adjuvant and boosted intraperitoneally 3 times thereafter at 3-week intervals with 100 μg of the same antigen in incomplete Freund's adjuvant. On days 3 and 2 before the fusion, mice were boosted with 100 μg PHF-tau in saline.

Mouse spleen cells were fused with SP2/0 myeloma cells, using a modified procedure of Kohler and Milstein (1975), with PEG 4000.

The cells of the fusion experiment were suspended at a density of 4.5×10⁴ spleen cells/well on 96-well plates preseeded with mouse peritoneal macrophage cells as a feeder layer. These wells were screened after 12 days for anti-tau antibody production in a sandwich ELISA either specific for normal tau or for PHF-tau as discussed in section 3. below.

Hybridoma growth was in Dulbecco's modified Eagle's medium (DMEM) supplemented with 20% fetal calf serum, sodium pyruvate (1 mM), L-glutamine (2 mM), penicillin (100 U/ml), streptomycin (100 mg/ml), and nonessential amino acids. All products were purchased from Gibco, (Paisley, U.K.). Cells were incubated in a humidified CO₂ -air incubator.

3. Sandwich ELISA for antibody screening

The screening ELISA used for the detection of anti-tau monoclonal antibodies was a sandwich ELISA system with affinity-purified polyclonal rabbit anti-human tau antibodies (Mercken et al; 1992a) in the coating phase. To this end, purified human normal tau, prepared as described in Mercken et al. (1992a) was used for the preparation of an immuno-affinity column using cyanogen bromide-activated Sepharose (Pharmacia, LKB Sweden). The affinity-bound anti-tau fraction was eluted from this column with a 0.1M citric acid buffered solution at pH 2.5. After neutralization, the anti-tau-containing fractions were pooled and coated overnight (1 μg/ml) at 4° C. on high-binding microtiter plates (Nunc, Gibco, Paisley, UK) in coating buffer (10 mM Tris, 10 mM NaCl, 10 mM NaN₃, pH 8.5). After overcoating for 30 min with 125 μl 10%-saturated casein in PBS to reduce non-specific binding, the plates were incubated with 100 μl of an appropriately diluted PHF-tau preparation and incubated for 60 min at 37° C. The plates were washed 3 times with PBS-0.05% Tween 20 (v/v); 100 μl hybridoma supernatant was added and incubation was continued for 1 h at 37° C. After washing, the bound monoclonal antibodies were detected with peroxidase-conjugated rabbit anti-mouse serum (Dakopatts, Glostrup, Denmark). All reagents were diluted in PBS with 10% casein. After final washing, 100 μA 0.42 mM 3,5,3',5'-tetramethylbenzidine, 0.003% H₂ O₂ v/v in 100 mM citric acid, 100 mM disodium hydrogen phosphate, pH 4.3, was added as peroxidase substrate. The reaction was stopped with 50 μl of a 2M H₂ SO₄ solution. Absorbance was read in a Titertek Multiscan (Flow Laboratories, Eflab, Oy, Finland) at 450 nm.

The cross-reactivity of the monoclonal antibodies with normal tau in ELISA was tested in a sandwich ELISA identical to the screening assay, except that affinity-purified normal tau was used as the antigen instead of PHF-tau.

At the first selection of positive hybridoma cultures, most positive cultures were initially composed of mixed clones as seen by visual inspection of the wells (3-4 clones per well). These positive cultures were arbitrarily designated AT1 to AT24 (some of these hybridoma cultures, i.e., AT1 to AT14 were described by Mercken et al., 1992b). After this initial screening round, hybridoma cultures were subcloned by limiting dilution, a technique well-know to those skilled in the art, finally resulting in pure hybridoma clones secreting antibodies with a homogeneous idiotype. These pure hybridoma clones were further tested with respect to their reactivity pattern on normal and PHF-tau in ELISA, Western blotting and immunohistochemistry, and to their capability to diagnose neurological diseases by means of their affinity for tau protein present in an undiluted sample of cerebrospinal fluid. Based on these criteria, the monoclonal antibody AT120 was selected and further characterized as shown in the following examples.

4. Determination of the antibody class and subclass

The antibody class and subclass was determined by Inno-LIA (Innogenetics, Ghent, Belgium). The antibody of the invention, AT120, appeared to be of the IgG1, kappa subtype.

Example II

Detection of pathological tau and normal tau in ELISA and by Western blotting

1. Detection of normal tau in ELISA using AT120.

Protein G-purified monoclonal antibody AT120, obtained from serum-free hybridoma AT 120 conditioned medium, was coated on ELISA plates and reacted with different dilutions of affinity-purified human normal tau as described in Mercken et al. (1992a), prepared in a solution of PBS and 10% casein.

The purity of normal tau was determined by SDS-PAGE. Tau samples were analyzed on an 420 A/H amino acid analyzer (Applied Biosystems B.V., Maarssen, The Netherlands) according to the manufacturer's instructions and the protein showed the expected amino acid composition. From the amino acid composition and by comparison with a standard peptide the concentration of normal tau was determined.

After incubation of the ELISA plates with different concentrations of tau spiked in tau- and PHF-tau-negative CSF for 1 h at room temperature, the plates were washed and incubated with 0,2 μg/ml biotynilated BT2 and HT7, each recognizing an epitope different from the AT120 epitope and present on normal term. After washing, complexed biotynilated antibodies were detected with horseradish peroxidase conjugated streptavidine (Jackson) and color development as specified in example I. The results are shown in Table I and FIG. 3.

                  TABLE I                                                          ______________________________________                                         Detection of normal tau in ELISA                                                             ABSORBANCE                                                       CONCENTRATION (expressed as milliabsorbance units)                             (pg/ml)       PHF-tau     normal tau                                           ______________________________________                                         160           1682        1609                                                 80            901         970                                                  40            566         678                                                  20            257         256                                                  10            143         154                                                   0             92          87                                                  ______________________________________                                    

2. Detection of pathological tau and of normal tau in Western blotting using AT120.

Purified normal human tau and PHF-tau were applied to 10% SDS-polyacrylamide gels and run under denaturing conditions according to Laemmli (1970). After SDS-PAGE, the transfer to nitrocellulose (Hybond-C, Amersham, Brussels, Belgium) was carried out in 10 mM NaHCO₃, 3 mM Na₂ CO₃, pH 9.9 for 120 min at 55V with cooling. After blotting, the nitrocellulose was equilibrated to phosphate buffered saline (PBS), and protein binding sites were blocked with blot buffer (PBS supplemented with 5% w/v skimmed dried milk and 10% v/v newborn calf serum). Blotted proteins were incubated overnight at 4° C. with AT120 as primary antibody. After 3 washings with PBS-0.05% Tween 20(v/v), horseradish peroxidase-labeled rabbit anti-mouse immunoglobulins (Dakopatts, Glostrup, Denmark) were used at a dilution of 1/3000 and were incubated for 90 min at room temperature. All antisera were diluted in blot buffer. The blots were then washed three times in PBS/Tween and developed with substrate solution (PBS,0.05% w/v 3,3'-diaminobenzidine, 0.03% v/v H₂ O₂) after which the reaction was stopped in H₂ O. Results shown in FIG. 1 indicate that the AT120 antibody recognizes all tau isoforms. By contrast, the Tau-1 antibody (Binder et al., 1985) reacts solely with normal tau, and the AT8 antibody (Mercken et al., 1992b) only with PHF-tau.

AT120, AT8 and Tau-1 mAbs were tested for phosphatase sensitivity of their epitopes in ELISA and in Western Blot on PHF-tau antigen. The reactivity of the AT120 antibody with PHF tau was not sensitive to phosphatase treatment either in ELISA (data not shown) or on Western blots (data not shown). The reactivity of AT8 was almost completely abolished after alkaline phosphatase treatment of the PHF-tau antigen in ELISA. Dephosphorylation of PHF-tau enhanced Tau-1 immunoreactivity, as described previously (Binder et al., 1985).

Example III

Detection of tau by immunohistochemistry

Paraffin sections of formalin-fixed brain tissue from neocortex, hippocampus, cerebellum, pons, and spinal cord of several Alzheimer patients and age-matched controls were prepared, as well as sections of peripheral nerve from one control patient.

Cryostat sections from Alzheimer and age-matched control brain were also prepared. Tissues were immunostained either with the peroxidase-antiperoxidase (PAP) technique (Steinberger et al., 1970) or with the avidin-biotin complex (ABC) technique (Hsu et al., 1981) using Dakopatts (Denmark) and Amersham (UK) reagents, respectively.

Briefly, after blocking non-specific interactions with normal swine serum (Dakopatts X901) diluted 1:25 in Tris-buffered saline (TBS) containing 1% bovine serum albumin (BSA), sections were incubated overnight with the AT120 primary antibody appropriately diluted in TBS/BSA. Secondary antibody and peroxidase complex were then applied for 30 min each, with intermediate rinsing in TBS. Color was developed with 3,3'-diaminobenzidinetetrahydrochloride (Sigma). Sections were counterstained with Harris' hematoxylin, dehydrated, coverslipped, and viewed under a light microscope.

FIGS. 2A and 2B clearly indicate that AT120 produces abundant staining of NFT, dystrophic neurites in plaques, and dispersed staining of neuropil (neuropil threads).

Example IV

Detection of tau in cerebrospinal fluid samples

Cerebrospinal fluid samples

CSF samples from patients were collected at the Department of Neurology of the University Hospital of Antwerp. All samples were obtained by lumbar puncture performed for routine diagnostic purposes. CSF samples were frozen and kept at -75° C. in small aliquots until use.

The patients were divided into 3 different groups: 27 patients diagnosed with probable AD according to Mc Khann et al. (1984), mentally healthy control patients, who underwent lumbar puncture for radiculopathy and patients suffering from other neurological diseases (OND). The OND group included inflammatory, vascular, and other diseases, including patients with neurodegenerative diseases such as adenoleukodystrophy, frontal lobe degeneration, cerebellar atrophy, olivo-ponto-cerebellar atrophy, and amyotrophic lateral scelerosis. The age, sex and diagnosis were noted for each patient.

AT120 assay

AT120 monoclonal antibodies purified from serum-free conditioned medium by Protein G column chromatography were coated overnight at 4° C. on high-binding microtiter plates (Nunc, Gibco, Paisley, UK) in coating buffer at 3 μg/ml (10 mM Tris, 10 mM NaCl, 10 mM NaN₃, pH 8.5). After overcoating for 30 min with 150 μl 10%-saturated casein in PBS to reduce non-specific binding, the plates were incubated with 25 μl CSF and 75 μl conjugate mixture containing 0.2 μg/ml of biotynilated BT₂ and an equal amount of HT7 in 5% Tween 20, 10% saturated casein in PBS. The plates were left overnight at room temperature and after washing peroxidase conjugated streptavidine (Jackson) (1/15000) was added for 30 minutes at room temperature.

Following an additional washing, 100 μl 0.42 mM 3.5, 3', 5'-tetramethylbenzidine 0.003% H₂ O₂ v/v in 100 mM citric acid, 100 mM disodium hydrogen phosphate, pH 4.3, were added as perocidase substrate. The reaction was stopped with 50 μl of a 2MH₂ SO₄ solution. Absorbance was read in a Titertech Multiscan (Flow laboratories, Eflab, Oy, Finland) at 450 nm.

Absorbance values obtained with AT120 from the CSF samples were compared with standard curves generated from known quantities of affinity purified normal human tau and this comparison allowed the result to be expressed as pg tau/ml.

A summary of these results are compiled in Table II, where patients ID, diagnosis, age and tau values expressed in pg/ml CSF are listed. From these results, it is obvious that levels of control patients are substantially lower (mean : 16.4 pg/ml) as compared to the group of patients suffering from various neurological diseases (OND; mean value: 26.4 pg/ml). For patients with Alzheimer's disease the mean value is clearly elevated above those of control and OND samples (mean Alzheimer patient : 50.8 pg/ml). If a cut-off level of 27 pg/ml is adapted, 8% of the control samples are positive, while for the OND group and the Alzheimer group these values are 27% and 80% respectively.

                  TABLE II                                                         ______________________________________                                         Mean Tau levels as determined with the AT120 ELISA assay, grouped              according to control patients, Alzheimer patients (AD) and other               neurological diseases (OND) and according to age cohhort.                      Number Diagnosis        Age    pg/ml mean Std                                  ______________________________________                                         3      AD (early onset AD)                                                                             35     *56.5 33.3 12.3                                 260    A.D.             41     *31.2                                           113    A.D.             44     *42.6                                           161    A.D. (possibly Crentzfeld)                                                                      57     *33.8                                           81     A.D.             58     *14.5                                           126    A.D.             59     *24.8                                           421    A.D.             59     *29.8                                           338    A.D.             64     *51.2 61.68                                                                               35.4                                 254    A.D.             66     *80.2                                           209    A.D.             67     *74.4                                           383    Primary degenerative                                                                            67     *32.5                                                  dementia                                                                38     A.D.             67     *68.7                                           229    A.D.             73     *70.9                                           132    A.D.             76     *51.9                                           88     A.D.             76     *25.3                                           65     Dementia         77     *80.1                                           71     A.D.             78     *53.9                                           28     A.D. (early onset A.D.)                                                                         78     *48.7                                           11     A.D.             85     *14                                             39     A.D.             86     *150                                            386    control           5     *17.5 17.3 4.37                                 108    control          20     *14.3                                           402    control          26     *14                                             106    control          27     *14                                             424    control          28     *14                                             355    control          28     *20.1                                           399    control          29     *14                                             373    control          30     *17.4                                           381    control          31     *14                                             372    control          32     *19.2                                           379    control          32     *18.3                                           241    control          32     *14                                             415    control          32     *14                                             428    control          33     *16.6                                           118    control          34     *21.5                                           224    control          36     *15.7                                           24     control          37     *25.2                                           369    control          38     *23.9                                           425    control          39     *14                                             145    control          40     *31.9                                           61     control          40     *17.3                                           377    control          40     *14                                             366    control          41     *17.7                                           401    control          41     *20.1                                           400    control          42     *14                                             417    control          42     *14                                             354    control          43     *16.8                                           34     control          43     *25.8                                           217    control          43     *14                                             364    control          44     *14                                             134    control          45     *16.7                                           367    control          45     *14                                             427    control          45     *14                                             394    control          48     *14                                             361    control          48     *14                                             237    control          50     *17.2                                           396    control          52     *16.4                                           100    control          54     *23.9                                           411    control          54     *14                                             371    control          55     *18.4                                           423    control          56     *14.9                                           99     control          56     *27.9                                           192    control          60     *19.9 24.83                                                                               15.17                                387    control          61     *14                                             389    control          65     *19.5                                           426    control          66     *15.4                                           141    control          67     *14                                             368    control          67     *15.4                                           60     control          77     *43.5                                           348    control          80     *56.9                                           419    Hdrocephalus      0     *150  29.35                                                                               26.78                                413    Adenoleukodystrofy                                                                              13     *23.1                                           376    Paresthesia      14     *21.1                                           239    Epilepsy, encephalitis                                                                          16     *29.8                                           7      SSPE             17     *48.1                                           139    Cerebellitis (Mycoplasma p.)                                                                    18     *19.7                                           180    Herpes encephalitis                                                                             19     *14.1                                           206    GBS              20     *15.9                                           140    TC ?             21     *14.2                                           228    Ishernic cerebral infarct                                                                       22     *150                                            197    Kawasaki         24     *27.8                                           133    MS               24     *37.1                                           212    Alcohol PNP      25     *14                                             66     MS ?             25     *14                                             143    Myopathy         25     *18.3                                           82     MS               26     *20.2                                           258    Guillian-Barre   26     *14.4                                           105    MS               26     *18.4                                           169    Dementia ?       27     *37.5                                           351    Viral meningitis 28     *17.3                                           213    MS               28     *15.7                                           253    Encephalitis viral ?                                                                            28     *38.1                                           236    Migraine         29     *17.3                                           405    Guillian-Barre   29     *47.6                                           72     MS               29     *14                                             234    MS               29     *19.9                                           128    GBS              29     *14                                             138    PNP              32     *17.6                                           218    Empty sella      35     *14                                             135    MS               35     *16.3                                           346    Neuritis optico  35     *14                                             117    Trigeminus neurology                                                                            36     *14                                             350    MS               37     *14                                             384    Guillian-Barre   37     *14                                             123    CVA              38     *14                                             56     TIA (transient ischemic                                                                         39     *14.9                                                  attack)                                                                 172    CVA ? psych.     40     *21.7                                           189    Hemicranial headache                                                                            41     *15.9                                           119    Amyloidosis      42     *15.3                                           69     Meningitis       42     *26.5                                           231    Contuno alcohol  42     *15.5                                           130    External oftalmoplegia                                                                          43     *53.6                                           357    CVA              44     *16.6                                           391    MS               44     *14                                             62     MS ??            44     21.2                                            124    Syphilis         45     *20.4                                           89     PNP              45     *27.1                                           122    Cauda equina syndroom etiol.                                                                    46     *14                                             249    MS               47     *14                                             112    MS ?             48     *14.9                                           363    Encephalitis     48     *35.9                                           125    MS               48     *24.9                                           205    GBS              49                                                     388    MS               50     *14                                             418    Tetanos          50     *14                                             207    GBS ?            50     *70.3                                           114    Cellebella atrofy                                                                               51     *51.5                                           121    Syphilis         51     *28.1                                           35     MS + PNP (diabetic)                                                                             51     *17.3                                           215    OLM              52     *14                                             101    Brain infarct    53     *52.8                                           255    PNP + (MS ?), diabetic                                                                          53     *18.4                                           173    Lyme disease     54     *17.5                                           360    (Borrelia) (MS-like)                                                                            54     *34.7                                           374    ALS              54     *65.3                                           179    Lyme disease     54     *16.4                                           50     Epilipsy-alcoholism                                                                             55     *21.5                                           184    Epilepsia        55     *16.7                                           210    MS               56     *16.2                                           58     CVA              57     *25.3                                           137    Pick ?           57     *77.4                                           131    Meningial bleeding                                                                              57     *66.7                                           398    Meningoencephalis                                                                               58     *117.8                                          349    Meningoencephalis                                                                               58     *35.6                                           244    Facialis parese  58     *18.5                                           219    Pseudobullair syndrome                                                                          58     *39.6                                           64     MS               58     *40.7                                           36     TIA              59     *14                                             240    Guillian-Barre    68?   *14   25.06                                                                               15.69                                70     N. ulnaris/Parkinson (?)                                                                        60     *23.8                                           166    tbc              60     *14                                             85     Aneurism         60     *18.3                                           204    Bipyramidal idiop                                                                               60     *16.8                                           167    Cerebellar atrophy                                                                              61     *14                                             157    Bulbar paralysis 62     *17.4                                           30     Steele richardson                                                                               62     *19.2                                           153    Lymfoa CSZ       62     *22.2                                           414    Subacute polyneuropathy                                                                         62     *14                                             37     OPCA             63     *26.7                                           109    Pick; ALS        63     *40.5                                           277    COLD             64     *14                                             195    E, dialysis      64     *14                                             148    MS               65     *15.4                                           375    Polyneuropathy, Charot-                                                                         65     *15.5                                                  Marie-Tooth                                                             182    ALS              65     *14                                             230    Parkinson        66     *21.1                                           409    Multiple vascular (pons.)                                                                       66                                                     170    Temp. E          66     *24.2                                           186    ALS              66     *21.2                                           59     Menigeal aneurysma                                                                              67     *28.4                                           233    Korsakow-like post trauma                                                                       67     *29.6                                           120    ALS              67     *25.7                                           550    PNP, CVA, diabetis                                                                              67     *64.2                                           110    Diabetis         67     *14                                             259    Polyvascular syndrome +                                                                         68                                                            demyelinis                                                              248    (?)              68     *14                                             235    CVA              68     *77.9                                           362    Guillain-Barre   68     *14                                             208    PNP-zona         68     *28.8                                           115    Subacute combined                                                                               68     *14                                                    degeneration                                                            98     TIA              68     *34.9                                           193    GBS              68     *44.1                                           222    Guillain-Barre   69     *14.1                                           102    PNP              70     *14                                             242    Bipyramidal syndrom PNP                                                                         72     *20.8                                                  atio                                                                    251    Trauma cerebri commoti                                                                          77     *14                                             422    Infarct          78     *20.7                                           42     Multi-infarct dementia                                                                          78     *38.9                                           93     Diabetis, PNP, radiculopathy                                                                    85     *61.9                                           53     Mixed dementia, Parkinson                                                                       85     *59.3                                           ______________________________________                                          Abbreviations: SSPE: Subacute sclerosing panencephalitis, GBS:                 GuillainBarre syndrome, TC: Meningeal tuberculosis, MS: Multiple               sclerosis, PNP: Polyneuropathy, CVA: cerebrovascular amyloidosis, ALS:         Amyotrophic lateral sclerosis, TIA: Transient ischemic attack, OPCA:           Olivoponto cerebellar atrophy, COLD: Chronic obstructive lung disease.   

Example V

Definition of the AT120 epitope

Since AT120 reacts equally well with all isoforms of tau (Goedert et al., 1989), the smallest recombinant tau form was used for deletion mapping. To this, two sites were used for deletion construction, the SaclI site at position 155 of the human tau 34 sequence and the SmaI site position 220 (Goedert et al., 1989). mTNF-fusion vector pmTNF(MPH) (Innogenetics, Ghent, Belgium), in which the smallest tau open reading frame was fused to 25 amino acids of mouse tumor necrosis factor was cut with ApaI - SacII, blunted with T₄ DNA polmerase and ligated. After cutting the ligated material with Sac II and Apa I to reduce non-mutant background, the mixture was transformed into MC1061 pc I587 (Casadaban & Cohen, (1980)). Each selected clone was further characterized by restriction digestion and by its reactivity with anti-tau antibodies.

The same mouse TNF fusion tau vector was used to insert a frame shift mutation in the XmaI restriction site. The vector was cut with SmaI, blunted with T₄ DNA polymerase and the ligated mixture was retreated with SmaI before transformation in order to reduce non-mutant background. The reactivity pattern of each of the mutants was checked with AT120 monoclonal antibodies by means of Western Blotting. This allowed to localize the epitope of AT120 in a first approximation to the region of 65 amino acids at amino acid 155-221 (FIG.4). However, since in this region also two other antibodies, BT2 (Mercken et al, 1992a) and HT7 (Mercken, Ph.d. Thesis) show reactivity it was mandatory to prove that no competition binding was observed between the latter monoclonal antibodies and AT120.

Therefore, a competition ELISA with each of these antibodies was performed. To this, affinity purified rabbit anti-human tall polyclonal antibodies were coated overnight at 4° C. in coatingsbuffer (10 mM Tris pH 8.6, 10 mM NaCl, 10 mM NaN₃), and after blocking with 0,1% caseine in PBS 100 μl/well of pure PHF-tau was added for 1 h at 37° C. After washing, 50 μl of either AT8, BT2 or AT120 unlabeled monoclonal antibody was added at a concentration of 10 μl/ml and incubation was continued for 30 min at 37° C. Next, 50 μl of biotinylated monoclonal antibody was added. Each of these biotinylated antibodies was used in a preset concentration, which in a tau Sandwich ELISA, as described in Example II, gave 50% of the maximal OD value. After a subsequent incubation of 1 h at 37° C., the plates were further treated as described in Example II.

                  TABLE III                                                        ______________________________________                                                    Unlabeled competitor                                                           Absorbance                                                          BIOTINYLATED AT8         AT120   BT2                                           ______________________________________                                         AT8          0.001       0.372   N.D.                                          AT120        0.476       0.001   N.D.                                          BT2          N.D.        0.543   0.054                                         ______________________________________                                          N.D. refers to not determined absorbances                                

The results, shown in Table III clearly indicate that the epitope recognized by the monoclonal antibody AT120 is different from the epitopes recognized by the monoclonal antibodies BT2 and AT8. On the basis of their respective reactivity patterns, obtained by incubating solid phase immobilized synthetic nonapeptides, the sequence of which was derived from the epitope of the invention, with each of these monoclonal antibodies followed by visualization of the complexes as in Example I, section 3, it was confirmed that the epitope recognized by AT120 is different from that of each of the other monoclonal antibodies (Table IV and FIG. 5)

                  TABLE IV                                                         ______________________________________                                         Reactivity of monoclonal antibodies BT2, HT7 and AT120 with                    solid phase bound nonapeptides.                                                The nonapeptides are designated in the one-letter amino acid code.                         Detecting Monoclonal antibody                                                  Absorbance                                                         Nonapeptides  HT7         BT2    AT120                                         ______________________________________                                         GAAPPGQKG     3.00        0.168  0.089                                         (SEQ ID NO:7)                                                                  GDRSGYSSP     0.493       3.00   0.553                                         (SEQ ID NO:8)                                                                  ______________________________________                                    

In addition to these experiments, the AT120 epitope was also confirmed by peptide mapping. Hereto, a total of 20 ,μg of mTNF-MPHtau1 (see FIG. 6) was lyophilized and redissolved in 56 μl of 100 mM Tris HCI containing 10% acetonitrile. To this was added 14 μl of endoprotease Asp N (0.04 μg/ml) and the mixture was incubated for 8 hours at 37° C. Following cleavage, the mixture was divided equally over 5 sample wells and subjected to SDS-polyacrylamide gel electrophoresis. Following electrophoresis, the peptides in the gel were blotted onto a PVDF membrane. A strip of the PVDF membrane corresponding to one lane on the gel was removed. Free binding sites on the membrane were blocked by incubation with 0.5% casein in PBS, and the strip was incubated with the monoclonal antibody AT120 to determine if protein fragments were present which were capable of being recognized. The presence of bound antibody was detected using an alkaline phosphatase-labeled rabbit anti-mouse conjugate followed by incubation with 5-bromo-4-chloro-3-indolyl phosphate and nitro blue tetrazolium. The remainder of the PVDF membrane was stained with Amido Black, which revealed the presence of 5 bands, all with a molecular size smaller than that of the original protein. One of these bands was visible on the portion of the blot which was incubated with AT120. The band which was specifically recognized by AT120 corresponded to the largest of the Amido Black-stained bands with an apparent molecular size of approximately 6 kDa. This band was excised from the Amido Black-stained blot and subjected to amino terminal sequence analysis (Edman degradation). The analysis revealed that the band recognized by AT120 began with Asp193 in the amino acid sequence of tau, close to the C-terminus of the tau sequence contained within the mTNF-MPHtau1 recombinant protein.

As a result of the protein cleavage experiment, the following peptide was synthesized according to the methods detailed in PCT patent application published under No. WO 93/18054. ##STR3##

This protein was tested for antibody recognition in an ELISA after first binding the peptide to streptavidin-coated wells according to the methods outlined in patent application WO 93/18054. In initial experiments, no AT120 binding activity could be detected when the binding reaction was carried out in phosphate buffered saline. Because the lack of binding could be due to the possibility that the peptide was in an unfavorable conformation, the experiment was repeated in the presence of 25% trifluoroethanol (TFE). In this case, binding could be observed. The experiment was again repeated with a second peptide with the following sequence: ##STR4##

Again, antibody binding could be observed in the presence of trifluoroethanol, which further localizes the epitope recognized by AT120 to this sequence. A titration was performed using the peptide tau2B as antigen in order to determine the optimal TFE concentration, which indicated that antibody binding reaches an apparent maximum at 25% TFE.

Amino acid sequences located downstream with respect to R₂₂₁ may contribute to the conformational stability of the AT120 epitope. In order to test this hypothesis and at the same time further delineate the position of the sequence bound by this antibody, the following peptide was synthesized: ##STR5##

A comparative ELISA performed with this peptide together with the others gave the following results:

    ______________________________________                                                    tau2B     tau2|B  tau4B                                             ______________________________________                                         AT120 (no TFE)                                                                              0.066       0.066   >>>3.000                                      AT120 (25% TFE)                                                                             1.876       1.900   >3.000                                        ______________________________________                                    

The consensus sequence for the epitope recognized by AT120 therefore is: ##STR6## in which the sequence between brackets may confer additional stability to the epitope.

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    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 10                                                  (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 67                                                                 (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (ix) FEATURE:                                                                  (A) NAME/KEY: human tau protein 155- 211                                       (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                        ArgGlyAlaAlaProProGlyGlnLysGlyGlnAla                                           1510                                                                           AsnAlaThrArgIleProAlaLysThrProProSer                                           1520                                                                           SerGluGluProProLysSerGlyGluProProLys                                           253035                                                                         SerGlyAspArgSerGlyTyrSerSerProGlySer                                           4045                                                                           ProGlyThrProGlySerArgSerArgThrProSer                                           505560                                                                         LeuProThrProProThrArg                                                          65                                                                             (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 33                                                                 (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (ix) FEATURE:                                                                  (A) NAME/KEY: human tau protein 199- 231                                       (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                        SerProGlySerProGlyThrProTyrSerArgSer                                           1510                                                                           ArgThrProSerLeuProThrProProThrArgGlu                                           1520                                                                           ProLysLysValAlaValValArgThr                                                    2530                                                                           (2) INFORMATION FOR SEQ ID NO:3:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 23                                                                 (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (ix) FEATURE:                                                                  (A) NAME/KEY: human tau protein 199- 221                                       (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                        SerProGlySerProGlyThrProTyrSerArgSer                                           1510                                                                           ArgThrProSerLeuProThrProProThrArg                                              1520                                                                           (2) INFORMATION FOR SEQ ID NO:4:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 31                                                                 (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                        GlyGlyAspArgSerGlyTyrSerSerProGlySer                                           1510                                                                           ProGlyThrProGlySerArgSerArgThrProSer                                           1520                                                                           LeuProThrProProThrArg                                                          2530                                                                           (2) INFORMATION FOR SEQ ID NO:5:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 27                                                                 (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                        GlyGlySerGlyTyrSerSerProGlySerProGly                                           1510                                                                           ThrProGlySerArgSerArgThrProSerLeuPro                                           1520                                                                           ThrProPro                                                                      25                                                                             (2) INFORMATION FOR SEQ ID NO:6:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 35                                                                 (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                        GlyGlySerProGlySerProGlyThrProGlySer                                           1510                                                                           ArgSerArgThrProSerLeuProThrProProThr                                           1520                                                                           ArgGluProLysLysValAlaValValArgThr                                              253035                                                                         (2) INFORMATION FOR SEQ ID NO:7:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 9                                                                  (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:                                        GlyAlaAlaProProGlyGlnLysGly                                                    15                                                                             (2) INFORMATION FOR SEQ ID NO:8:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 9                                                                  (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:                                        GlyAspArgSerGlyTyrSerSerPro                                                    15                                                                             (2) INFORMATION FOR SEQ ID NO:9:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1173                                                               (B) TYPE: Nucleic Acid                                                         (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (ix) FEATURE:                                                                  (A) NAME/KEY: mTHFMPH-tau1 gene                                                (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:                                        ATGGTAAGATCAAGTAGTCAAAATTCGAGTGACAAGCCTG40                                     TAGCCCACGTCGTAGCAAACCACCAAGTGGAGGAGCAGGG80                                     AATTCACCATCACCATCACCACGTGGATCCCGGGCCCATG120                                    GCTGAGCCCCGCCAGGAGTTCGAAGTGATGGAAGATCACG160                                    CTGGGACGTACGGGTTGGGGGACAGGAAAGATCAGGGGGG200                                    CTACACCATGCACCAAGACCAAGAGGGTGACACGGACGCT240                                    GGCCTGAAAGCTGAAGAAGCAGGCATTGGAGACACCCCCA280                                    GCCTGGAAGACGAAGCTGCTGGTCACGTGACCCAAGCTCG320                                    CATGGTCAGTAAAAGCAAAGACGGGACTGGAAGCGATGAC360                                    AAAAAAGCCAAGGGGGCTGATGGTAAAACGAAGATCGCCA400                                    CACCGCGGGGAGCAGCCCCTCCAGGCCAGAAGGGCCAGGC440                                    CAACGCCACCAGGATTCCAGCAAAAACCCCGCCCGCTCCA480                                    AAGACACCACCCAGCTCTGGTGAACCTCCAAAATCAGGGG520                                    ATCGCAGCGGCTACAGCAGCCCCGGCTCCCCAGGCACTCC560                                    CGGCAGCCGCTCCCGCACCCCGTCCCTTCCAACCCCACCC600                                    ACCCGGGAGCCCAAGAAGGTGGCAGTGGTCCGTACTCCAC640                                    CCAAGTCGCCGTCTTCCGCCAAGAGCCGCCTGCAGACAGC680                                    CCCCGTGCCCATGCCAGACCTGAAGAATGTCAAGTCCAAG720                                    ATCGGCTCCACTGAGAACCTGAAGCACCAGCCGGGAGGCG760                                    GGAAGGTGCAAATAGTCTACAAACCAGTTGACCTGAGCAA800                                    GGTGACCTCCAAGTGTGGCTCATTAGGCAACATCCATCAT840                                    AAACCAGGAGGTGGCCAGGTGGAAGTAAAATCTGAGAAGC880                                    TTGACTTCAAGGACAGAGTCCAGTCGAAGATTGGGTCCCT920                                    GGACAATATCACCCACGTCCCTGGCGGAGGAAATAAAAAG960                                    ATTGAAACCCACAAGCTGACCTTCCGCGAGAACGCCAAAG1000                                   CCAAGACAGACCACGGGGCGGAGATCGTGTACAAGTCGCC1040                                   AGTGGTGTCTGGGGACACGTCTCCACGGCATCTCAGCAAT1080                                   GTCTCCTCCACCGGCAGCATCGACATGGTAGACTCGCCCC1120                                   AGCTCGCCACGCTAGCTGACGAGGTGTCTGCCTCCCTGGC1160                                   CAAGCAGGGTTTG1173                                                              (2) INFORMATION FOR SEQ ID NO:10:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 391                                                                (B) TYPE: Amino Acid                                                           (C) STRANDEDNESS: Unknown                                                      (D) TOPOLOGY: Unknown                                                          (ix) FEATURE:                                                                  (A) NAME/KEY: mTHFMPH-tau1 fusion protein                                      (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10:                                       MetValArgSerSerSerGlnAsnSerSerAspLys                                           1510                                                                           ProValAlaHisValValAlaAsnHisGlnValGlu                                           1520                                                                           GluGlnGlyIleHisHisHisHisHisHisValAsp                                           253035                                                                         ProGlyProMetAlaGluProArgGlnGluPheGlu                                           4045                                                                           ValMetGluAspHisAlaGlyThrTyrGlyLeuGly                                           505560                                                                         AspArgLysAspGlnGlyGlyTyrThrMetHisGln                                           6570                                                                           AspGlnGluGlyAspThrAspAlaGlyLeuLysAla                                           7580                                                                           GluGluAlaGlyIleGlyAspThrProSerLeuGlu                                           859095                                                                         AspGluAlaAlaGlyHisValThrGlnAlaArgMet                                           100105                                                                         ValSerLysSerLysAspGlyThrGlySerAspAsp                                           110115120                                                                      LysLysAlaLysGlyAlaAspGlyLysThrLysIle                                           125130                                                                         AlaThrProArgGlyAlaAlaProProGlyGlnLys                                           135140                                                                         GlyGlnAlaAsnAlaThrArgIleProAlaLysThr                                           145150155                                                                      ProProAlaProLysThrProProSerSerGlyGlu                                           160165                                                                         ProProLysSerGlyAspArgSerGlyTyrSerSer                                           170175180                                                                      ProGlySerProGlyThrProGlySerArgSerArg                                           185190                                                                         ThrProSerLeuProThrProProThrArgGluPro                                           195200                                                                         LysLysValAlaValValArgThrProProLysSer                                           205210215                                                                      ProSerSerAlaLysSerArgLeuGlnThrAlaPro                                           220225                                                                         ValProMetProAspLeuLysAsnValLysSerLys                                           230235240                                                                      IleGlySerThrGluAsnLeuLysHisGlnProGly                                           245250                                                                         GlyGlyLysValGlnIleValTyrLysProValAsp                                           255260                                                                         LeuSerLysValThrSerLysCysGlySerLeuGly                                           265270275                                                                      AsnIleHisHisLysProGlyGlyGlyGlnValGlu                                           280285                                                                         ValLysSerGluLysLeuAspPheLysAspArgVal                                           290295300                                                                      GlnSerLysIleGlySerLeuAspAsnIleThrHis                                           305310                                                                         ValProGlyGlyGlyAsnLysLysIleGluThrHis                                           315320                                                                         LysLeuThrPheArgGluAsnAlaLysAlaLysThr                                           325330335                                                                      AspHisGlyAlaGluIleValTyrLysSerProVal                                           340345                                                                         ValSerGlyAspThrSerProArgHisLeuSerAsn                                           350355360                                                                      ValSerSerThrGlySerIleAspMetValAspSer                                           365370                                                                         ProGlnLeuAlaThrLeuAlaAspGluValSerAla                                           375380                                                                         SerLeuAlaLysGlnGlyLeu                                                          385390                                                                         __________________________________________________________________________ 

We claim:
 1. The hybridoma AT 120l deposited at ECACC on Oct. 8, 1992 under No. 92-100853 which secretes monoclonal antibody AT120.
 2. Monoclonal antibody AT120 secreted by hybridoma AT120 of claim
 1. 